The present invention relates to a switchgear for opening/closing an electrical circuit and its operating mechanism and, more particularly, to a switchgear and its operating mechanism suitably configured for cutting off high-voltage current in short time periods.
In general, there are available, as an operating mechanism of a switchgear, one using a hydraulic operating force for large power and one using a spring operating force for middle/small output power. The former is referred to as “hydraulic operating mechanism” and the latter as “spring operating mechanism”. In recent years, the advancement of miniaturization of an arc-extinguishing chamber of a gas-insulated circuit breaker which is a type of a switchgear allows fault current to be broken with a smaller operating force, so that application of the spring operating mechanism becomes popular. However, a gas-insulated circuit breaker of extra high-voltage class requires high-speed operating capability called “2 cycle operation” that is capability of achieving opening within a time length corresponding to two-cycle time periods of alternating current. A conventional spring operating mechanism typically has operating capability equivalent to about 3 cycle operation, and it is not easy to realize the two-cycle opening capability due to poor responsiveness of a retention mechanism or retention control mechanism of a spring force.
A first type of conventional example of an operating mechanism of such a switchgear is disclosed in Japanese Patent Application Laid-Open Publication Nos. 11-213824 and 2000-40445 (the entire contents of which are incorporated herein by reference). In operation mechanisms disclosed in these documents, a force of a opening spring is retained by a retention mechanism constituted by a latch, O-prop (opening-hook lever), and a catch through an output lever. In this configuration, when a trip current is applied to a solenoid serving as a retention control mechanism, a plunger of the solenoid activates the catch to allow the engagement between the catch and prop to be released, which releases the engagement between the output lever and the latch to rotate the output lever to release the opening spring force, thereby achieving opening operation.
A second type of conventional example of the switchgear operating mechanism is disclosed in Japanese Patent No. 3497866 (the entire content of which is incorporated herein by reference). In a spring operating mechanism disclosed in this document, a pull-out lever and a retention lever are provided for retaining a opening spring force. In this configuration, the retention lever is activated not by the opening spring force but by a force of an acceleration spring at the opening operation time so as to release the opening spring force.
In the first type of conventional example, operation for releasing the opening spring force (opening operation) is constituted by the following three steps: operation of the catch driven by excitation of the solenoid, operation of the O-prop, and operation of electrical contacts including the opening spring. The operational relationship between the above components is shown in FIG. 10. The horizontal axis denotes time, and vertical axis denotes a stroke of each components. The lowermost curve represents the waveform of a trip current and, above this, the stroke of the catch is shown. Above this, the strokes of the O-prop and opening spring are shown. The uppermost curve represents an energizing signal of the contact in an arc-extinguishing chamber of a gas-insulated circuit breaker.
Time length from the start of application of the trip current until the operation of the O-prop is started along with the operation of the catch is assumed to be T1. Time length from the start of operation of the O-prop to the start of operation of the opening spring is assumed to be T2. Time length from the start of operation of the opening spring until the opening spring reaches its contact parting point is assumed to be T3. Assuming that contact parting time is T0,T0=T1+T2+T3  (1)is satisfied.
In order to realize 2 cycle operation, it is necessary to reduce contact parting time T0 to a given value. As is clear from FIG. 10, in a typical spring operating mechanism, operations of the components from the catch to the opening spring, which occur after the trip current application, are not started simultaneously. That is, the catch operates to some degree to release the engagement between itself and O-prop to thereby allow operation of the O-prop to be started, and opening spring starts operating after the O-prop operates to some degree. Thus, a mechanism that retains a opening spring force operates in a stepwise manner, so that it is necessary to reduce respective time lengths T1, T2, and T3 in order to reduce T0.
However, since the opening spring force is determined by the weight of a movable portion of the arc-extinguishing chamber, opening speed, and drive energy, there is a limit to a reduction of T3. With regard to T2, weight reduction of the O-prop and increase in a force (retention force) of retaining the opening force allows high-speed operation of the O-prop. However, when the retention force is increased, the size of the O-prop needs to be increased for strength, which limits the weight reduction of the O-prop. It follows that there occurs a limit in the improvement in operation speed relying on the increase in the retention force. Further, when the retention force is increased, a large force is applied to the engagement portion between the O-prop and catch, so that there occurs a need to increase the size of the catch for strength and to provide a solenoid having a large electromagnetic power for activating the catch.
At present, an excitation method using a large-sized condenser is adopted for obtaining a large power of the solenoid. However, the upper limit value for a current value flowing to the solenoid is specified in the standard, so that there is a limit in the improvement in the output power of the solenoid. As described above, it is difficult to reduce the contact parting time in the conventional spring operating mechanism.
Also in the second conventional example, operation for releasing the opening spring force is constituted by the following three steps: operation of a pull-off hook driven by an electromagnet; simultaneous operation of a reset lever, acceleration spring, and retention lever; and simultaneous operation of a pull-off lever and opening spring. In this example, the direction of a retention force (pressuring force) of the opening spring is made substantially coincident with the rotation center of the retention lever, thereby reducing a force required for the operation of the retention lever.
Further, the speed of movement of the retention lever, which is included in the above second step, is made higher by the accelerating spring to thereby reduce the operation time. However, it is physically difficult to reduce the operation time of the second step to zero and, therefore, it is difficult to significantly reduce the entire contact parting time, also in terms of the problems described in the first example.
Further, the direction of a pressuring force to a portion at which the pull-off lever and retention lever are engaged with each other is made substantially coincident with the rotation center of the retention lever, so that when an external vibration is applied to the retention lever to force the same to vibrate, the pull-off lever is rotated in the opening operation direction, and the opening operating mechanism may start operating without an opening command. Further, the direction of the pressuring force fluctuates with respect to the rotation center of the retention lever due to deformation of the engagement surface between a roller provided on the pull-off lever and the retention lever, so that when the pressuring force acts in the opening operation direction of the retention lever, the pull-off lever may be released without an opening command.
Further, although not described in Patent Document 3, it is just conceivable that the retention lever operates in the opening direction due to an impact force applied when the roller pushes aside the retention lever for reengagement in the closing operation to allow the opening operation to be started without an opening command. As described above, in the second example, it is difficult to significantly reduce the contact parting time and it is likely that a retention state of the opening spring becomes unstable.